The invention relates to method and apparatus for cleaning a rubber coated cylinder mounted in an offset printing machine for transferring the print from a printing plate cylinder to a paper web running in contact with the rubber coated cylinder while the offset printing machine is running.
During printing the rubber coated cylinder will be contaminated by ink residues, paper dust, and paper fibers being deposited on and adhering to said cylinder, and as a consequence thereof it is necessary to clean the surface of the cylinder at regular intervals in order to maintain the quality of the print. The cleaning is effected by using a washing liquid (detergent, solvent, water, or a mixture thereof) and can be effected manually when the offset printing machine is not running, which, of course, means production lose. This can be avoided by manual cleaning while the offset printing machine is running, which also is practised but is dangerous due to the high rotational speed of the cylinder. Therefore, automatic systems have been proposed which at intervals clean the rubber coated cylinder while the offset printing machine is running. One method is to spray the cylinder with washing liquid in order to dissolve and wash off the contaminants, which means that large amounts of inflammable washing liquid that is not at all pro-environmental has to be handled in order to completely clean the cylinder, which is not satisfactory. Such a prior art cleaning system is disclosed in U.S. Pat. No. 5,303,652 and comprises a ramp mounted in parallel with the cylinder and having a number of spray nozzles distributed along the ramp for sprinkling the surface of the rubber coated cylinder with cleaning liquid under the rotation of the cylinder.
According to another prior art method, DE-A1 43 30 257, a rotating brush contacting the rubber coated cylinder is used, the rotational axis of said brush being parallel with the rotational axis of the cylinder. The brush is moistened with washing liquid. In order to avoid too hard wear of the rubber coating an effective cleaning of the cylinder at the same time being achieved, the cylinder then is wiped off by means of a cloth impregnated with washing liquid. The system is complicated with respect to construction as well as function.
The object of the invention is to provide an effective cleaning of the rubber coated cylinder while the offset printing machine is running, a reduced amount of washing liquid due to the fact that the contaminants are not washed off the cylinder but are brushed loose under gentle mechanical treatment of the rubber coating in order to loosen also firmly adhering contaminants, the washing liquid and the contaminants then being removed by means of the running paper web.
According to the invention said object is achieved by the method according to claim 1. The invention also relates to an apparatus for working the method according to claim 2.
While the off set printing machine is running and the rubber coated cylinder thus is rotating with the paper web running over the cylinder the contaminants on the cylinder are loosened and distributed by means of the reciprocating brush and are dissolved by means of the sprinkled washing liquid the contaminants together with the washing liquid being carried along by the rotating cylinder and removed in known manner from the offset printing machine by means of the paper web passing through the machine and bringing along washing liquid and contaminants from the cylinder at contact therewith.
The cleaning will be particularly effective if the brush comprises two sections located one behind the other in respect of the rotational direction of the cylinder, the first section loosening contaminants and the other section scraping loose such material as has not been removed in the first step, and distributing the contaminants over the surface of the cylinder.